Surge current protection circuit for small currents - has voltage divider with base capacitor operating thyristor controlling protection relay

摘要

The current transformer for small currents, e.g. between 10 and 500 mA, has a protective relay circuit against stray currents, or surges. The secondary winding (1) of the input transformer is followed by a rectifier bridge (2) and at the output is a relay (7) operated by a thyristor (6). Across the output of the rectifier bridge is a capacitor (3). This is followed by a voltage divider (4) so as to operate the thyristor when a given voltage is reached. The voltage divider consists of a capacitor followed by a blocking diode (8) a choke (11) and a base connecting capacitor (5) all in parallel with the rectifier output. In parallel with the base capacitor is a resistance (9).